1. Field of the Invention
The present invention relates to a process for the desulfurization of sulfur-containing hydrocarbon oils. More particularly, it relates to a hydrodesulfurization process wherein a sulfur-containing heavy hydrocarbon oil is treated with hydrogen and steam in the presence of a hydrodesulfurization catalyst.
2. Description of the Prior Art
Hydrodesulfurization processes in which heavy petroleum distillates or residual fractions are treated with hydrogen in the presence of a catalyst comprising a hydrogenation component composited with a refractory support are well known (see, for example, U.S. Pat. Nos. 3,531,398 and 3,509,044). It is also known to mix a hydrocarbon oil with from 2 to 30 percent by weight of water and to react the resulting mixture in contact with the catalyst under hydrodesulfurization conditions (see, for example, U.S. Pat. No. 3,501,396). A disadvantage of such a prior art procedure of injecting the water into the oil feed and vaporizing it or, alternatively, generating steam at the desulfurization unit operating pressure is that the vapor pressure of the steam will approach the desulfurization unit operating pressure and that additional heat of vaporization must be supplied at temperatures in the range of 500.degree. to 700.degree. F. At this temperature level, the heat absorbed by the water must be supplied by a furnace, thus incurring high investments of equipment. In addition, there is a substantial recurring fuel cost for supplying the heat of vaporization.
U.S. Pat. No. 2,606,141 discloses that water or water vapor may be injected into a hydrogen recycle gas stream prior to mixing the gas stream with the hydrocarbon oil which is to be vaporized for subsequent desulfurization.
U.S. Pat. No. 3,719,588 teaches the addition of steam to a carbon monoxide-containing reactant gas utilized in a hydrodesulfurization process.
An improved method of generating the steam desired in the hydrodesulfurization stage has now been found.